A group III-V compound semiconductor is widely used as a material of various semiconductor elements such as a light emitting element, e.g., a semiconductor laser diode (LD) and a light emitting diode (LED), and a logic circuit element, e.g., a field effect transistor (FET) and a heterojunction bipolar transistor (HBT). In these devices, a plurality of semiconductor layers having different mixed crystal compositions are layered together to realize intended optical and electrical characteristics.
A semiconductor device made of such a group III-V compound semiconductor requires a thickness control on the nanometer order and an interface steepness, and is thus typically manufactured by using a metal organic vapor phase epitaxy (MOVPE) method or a molecular beam epitaxy (MBE) method.
Particularly, AlxGayIn1-x-yP (where 0≦x≦1, 0≦y≦1, 0≦x+y≦1) and AlzGa1-zAs (where 0≦z≦1), which have band gaps corresponding to the visible region and the infrared region, respectively, are important semiconductor materials of light emitting elements. Furthermore, the band gaps can be varied over a wide range by varying the respective Al contents, and the electrical and optical characteristics of a semiconductor device using these materials can be variously adjusted by combining an AlGaInP layer and an AlGaAs layer. In this way, it is possible to realize a high-performance semiconductor device having a new function. Thus, the development of a group III-V compound semiconductor including an AlGaInP layer in combination with an AlGaAs layer is very important.
In view of this, the present inventor produced a group III-V compound semiconductor as illustrated in FIG. 25 by using an MOVPE method. As illustrated in FIG. 25, the group III-V compound semiconductor produced by the present inventor includes an AlGaInP layer 202 made of Al0.35Ga0.15In0.5P having a thickness of about 0.2 μm and an AlGaAs layer 203 made of Al0.6Ga0.4As having a thickness of about 0.3 μm, which are deposited in this order on a substrate 201 made of GaAs.
However, the group III-V compound semiconductor is observed, with human eyes, to be cloudy across the entire surface thereof, indicating occurrence of crystal defects. Further microscopic observation reveals that there are a large number of crystal defects having a diameter of about 1 μm with a density of 1.4×105/cm2. This is three to four orders of magnitude greater than the value obtained when only one layer of the AlGaInP layer 202 or the AlGaAs layer 203 is formed on the substrate 201 made of GaAs. This suggests that the occurrence of the crystal defects is due to the interface between the AlGaInP layer 202 and the AlGaAs layer 203.
Moreover, when the AlGaAs layer 203 is formed on the substrate 201, and the AlGaInP layer 202 is formed on the AlGaAs layer 203, such crystal defects are hardly observed. This suggests that the crystal defects are characteristic of a structure where the AlGaAs layer 203 is formed on the AlGaInP layer 202.
The crystal defects occur due to the fact that among interactions between an element of the AlGaInP layer 202 and an element of the AlGaAs layer 203, the interaction between the GaP component and the AlAs component is stronger than interactions between other elements or between atoms.
Specifically, in the step of growing the AlGaAs layer 203 on the AlGaInP layer 202 after the AlGaInP layer 202 is formed on the substrate 201, sufficient migration of the AlAs component in the AlGaAs layer 203 being grown is inhibited by the interaction between the AlAs component with the GaP component of the AlGaInP layer 202, thereby disturbing the atomic arrangement at the interface between the AlGaInP layer 202 and the AlGaAs layer 203.
As described above, when a group III-V compound semiconductor is produced in which an AlGaAs layer is deposited on an AlGaInP layer, a large number of crystal defects occur. Therefore, it is difficult to realize a group III-V compound semiconductor, or a group III-V compound semiconductor device using the same, in which an AlGaAs layer is deposited on an AlGaInP layer.